(a) Technical Field
The present invention relates to a technique of correcting a resolver offset. More particularly, the present invention relates to a technique of correcting a resolver offset, in which a resolver offset used for motor control in eco-friendly vehicles such as hybrid vehicles and so forth can be measured and corrected simply.
(b) Background Art
Today, due to high oil prices and CO2 restrictions, research has been continuously carried out on eco-friendly vehicles, such as hybrid vehicles, pure electric vehicles, fuel cell vehicles, etc., which are capable of replacing conventional internal-combustion engine vehicles. These eco-friendly vehicles typically use an electric motor (traction motor) as a drive source. For the most part, a permanent-magnet synchronous motor having high power and high efficiency is typically used as the traction motor, e.g., a built-in permanent-magnet synchronous motor.
Eco-friendly vehicles also have mounted thereon an inverter system for motor control, and use a resolver for detecting an absolute angular position θ of a motor's rotator used for motor control. It is well known that the resolver is mounted on an integrated starter & generator (ISG) of a hybrid vehicle, as well as the traction motor.
FIG. 1 is a schematic diagram of a drive system of a hybrid vehicle. As shown in FIG. 1, the hybrid vehicle has a layout in which an engine 11, which is a drive source, a traction motor 14, and a transmission 15 between the traction motor 14 and a drive shaft 16 are arranged in a line. The traction motor 14 and the transmission 15 are serially connected to each other, and the engine 11 and the traction motor 14 are connected to each other with a clutch 13 interposed therebetween for power transfer, such that power transfer can be controlled according to the state of the clutch 13.
In addition, a motor for providing a rotational force (outputting a cranking torque) to the engine 11 during starting, that is, an ISG 12 is connected to the engine 11. In this structure, when the clutch 13 is disengaged, then the drive shaft 16 of the vehicle is driven only by the traction motor 14. When the clutch 13 is engaged, then the drive shaft 16 may be driven by the engine 11 and the traction motor 14.
When the clutch 13 is locked, the ISG 12 and the traction motor 14 may be rotated by the torque of the engine 11, and in this case, the engine 11, the ISG 12, and the traction motor 14 all rotate at the same speed. In this case, the ISG 12 and the traction motor 14 act as the load of the engine 11, such that a counter electromotive force is generated in the ISG 12 and the traction motor 14 and they operate as a power generator for charging the battery.
In the last stage of a vehicle production line, a rotator position offset of the traction motor and the ISG (i.e., a difference between the position of the rotator of the motor and the position of the rotator of the resolver) while the clutch is engaged and the engine is idling has to be measured and stored in a motor control unit (MCU). By doing so, the MCU may correct a resolver's output signal by the measured offset and thus, the accurate position of the rotator of the motor can be reflected in motor control.
The resolver, as mentioned previously, is used to measure the absolute angular position θ of the motor's rotator used for motor control with respect to a motor's stator, and in initial assembly of the motor and the resolver, the rotator position offset between the motor and the resolver is inevitable for several reasons such as assembly tolerance between the motor and resolver, the inaccuracy of the position of an internal coil of the resolver, etc.
Eventually, without correcting the resolver's output signal by the offset, reflection of the accurate rotator's position during motor control is impossible. For this reason, when assembly between the motor and the resolver is completed in the production process, the offset has to be measured and stored to accurately correct the output signal of the resolver.
When the ISG or the traction motor is replaced due to failure or when the MCU in which the offset for the resolver is stored is replaced, a resolver position offset for the traction motor or the ISG has to be re-measured and re-stored in the MCU again for accurate offset correction. In this case, measurement and storage of the resolver offset are mainly performed in a service center rather than in a vehicle production stage, and thus due to human error, the resolver offset may not be re-measured after replacement. Thus, unless the resolver offset is re-measured, the resolver offset has to be before starting the vehicle after replacement. In addition, since the resolver offset has to be measured during starting, the measurement of the offset should be performed fairly quickly.
However, in a conventional method which controls the current to 0 through PI control after starting of the engine and then measures the resolver offset, the motor's current dynamics are a time varying system. Thus, it is difficult to ensure that the current is accurately controlled to 0 through PI control and due to a change in the speed of the engine, the offset measurement value may not be correct. Furthermore, a conventional method which measures the resolver position offset without starting of the engine is a complex process and thus requires a lot of time to execute, degrading the efficiency of vehicle production.